58 replies to this topic

[grammady]

I've heard tires/stems leak less with Nitrogen vs. air. You can add air if necessary. Nitrogen particles are larger than air. Opinions?
It costs about $5 a tire to replace.

[dwightginnyputzke]

We love to travel all the beautiful mountain roads but we wait until we arrive at sea level to fill our tires because of the thicker air.

[smokeater75]

Hi grammady, I have been using nitrogen in my suv and cars as well as our motorhome for the past 4yrs. I found that in the auto's when the temps dropped that the low air warning lights were constantly going off. When I switched to nitrogen no more problems. I take our motorhome out every two weeks in the winter to run the generator and heat up the tranny and engine, I found that when the temperature was down in the -30 range that the fluctuating air pressure was a real problem. I switched to nitrogen after talking to a number of truckers and Denray tire here in Winnipeg and no more problems. When my wife Susan and I leave for Indio Ca. in the middle of Feb. its usually around -25, when we come home we have put on about 6000 miles. I run 110 in the front and 100 across the back and I have not had to add any nitrogen to the tires during the trip. That is my experience. Aside from the Nitrogen molecule being larger there is also less moisture in a filtered Nitrogen supply. You can get Nitrogen at any large truck tire center and if you need a top up and your a Costco member you can get it there. Good Luck smokeater75.

[wolfe10]

Pure physics/chemistry says that PSI change with temperature is exactly the same for Nitrogen and DRY, repeat DRY air. Both follow the ideal gas law: PV=nRT.

Now, air from one of those coin op pumps is a very different matter- most have no air dryer and as you would expect, water and water vapor are NOT gases and will change PSI quite a lot with temperature change compared with Nitrogen or dry air.

Brett

[Briarhopper]

OK. Semi dumb queston(s) from my struggling understanding: Since N = 78% and O = 21%, the PSI problems come from the 1% leftover, but thats the air we breathe. So, is compressing the 1% and turning some of it into liquid what creates the more expansive part of compressed air. Seems like the most it could do is get back to 1%. To further confuse the issue in my mind, compressed dry air is still 1% other stuff, so??????? I realize the ratio is across the atmosphere of the planet, so maybe its just an issue where the leftover is more than 1%.

How much PSI fluctuation difference is there between nitrogen and air in a tire from 50F to 90F?

We inflate tires to a cold PSI to perform properly at operating temperatues taking into account the increase in pressure. If nitrogen reduces the increase in PSI, should nitrogen filled tires be cold inflated to a higher PSI?

I think I'm missing something, Interesting topic though.

[QuiGonJohn]

I too am confused over a few points. Sorry if these sound dumb, but I'm still a RV newbie.

For one, I thought I was told nitrogen was better because it helped the tires last longer and not heat up as much while driving.

I have a good air compressor at my home and would gladly check the pressures and top off before each trip, except that right now, my tires are running with nitrogen. I bought the RV in early April, had to put tires on straight away, and the shop used nitrogen.

If item 1 is not true, then it would seem to me, switching to air, so I can keep/maintain a much better handle on tire pressure, would be more beneficial than having to take the RV somewhere to check tire pressure and top off, if needed, and having to pay for the nitrogen besides all the other inconveniences.

If anyone can shed more light on this, it would be helpful.

[jrwitt]

Air is over 75% nitrogen anyway. If you want the convience of topping off with your compressor, there is no harm in doing that. Since air is already mostly nitrogen, there is absolutely no problem with filling nitrogen-inflated tires with air. You will of course loose the advantage of having pure nitrogen. There is no need to remove the old nitrogen to convert back to air. I haven't heard the claim about running cooler with nitrogen, but many claim that your tires won't loose pressure as fast with nitrogen since the nitrogen atoms are larger than the other atoms/molecules that make up free air. Maybe the "running cooler" claim is based on the tires being more likely to be at the correct pressure. Low tire pressure definately leads to heat buildup. I guess the answer to your problem is to decide if it is worth the inconvience of having to find a nitrogen supplier to top off your tires vs. having to top off more often if you just run air. Hopefully, you will get replies from folks who due run pure nitrogen that can comment on how easy it is to find nitrogen suppliers.

Good luck!
Jack

[wolfe10]

Boyles Law and the Ideal Gas Law (google them) are CENTURIES OLD and are still true today-- irrespective of what sales literature says to the contrary.

Yes, there are a few advantages of Nitrogen over DRY air, such as slightly larger molecule so slightly less air loss over time and no Oxygen so no oxidation/rust.

BOTH Nitrogen and DRY air have major advantages over WET air-- that supplied by most small home compressors and those coin op air machines at convenience stores (THEY DON'T HAVE DRYERS ON THEM).

So, Nitrogen is great, but I would not pay a lot extra for it over DRY air. I refuse to air up my RV or car unless the air is DRY/there is an air dryer on the system. Perhaps if I lived in the desert SW this would not be an issue, but this time of year with the dew point in the 60-70's, it IS an issue.

[Koliver]

QuiGonJohn

You will have between 4 and 5 cu ft of air in each tire. Topping up will add some, but not likely more than 1 or 2 %, especially if Nitrogen leaks out more slowly than air. In that 1 or 2% will be 22% other than N, or .less than .5% of the total. I don't think you will detect the difference.

You can add an inexpensive dryer to your home compressor. I have one I bought at Princess Auto for a few $. Try Harbor Freight.

[Tireman9]

I think I covered most if not all the questions in my blog on Nitrogen.

Bretts comments on dry are are very appropriate.

[rogelling]

Water vapor is a gas, and as such it exerts a pressure. Under STP conditions, the partial pressure of water at sea level is equal to the atm pressure times the relative humidity. If you now take room air at say relative humidity of 60% and compress it under isothermic conditions, water will condense on the bottom of your pressurized container. Thus the amount of water vapor in the compressed gas will be significantly less than what you started with at sea level pressure. This is why you have to periodically drain the water from the bottom of your compressed air tank. The higher the pressure in the tank, the drier the air will be. Going from 1 atm (14.6 psi) to say about 120 psi removes most of the water vapor from the air, roughly from 60% to 6% relative humidity. If you increase pressure to say several 1000 psi as in a cylinder air tank or oxygen tank, the gas in the cylinder is virtually bone dry, close to zero water vapor pressure. That is why when you use oxygen it is bubbled through a water container to increase the water content of inspired gas.

[QuiGonJohn]

Tireman, can you update the link for the pocket sized air dryer you mentioned? I clicked the one in your blog and was taken to a Mini Lathe Tool Kit at Harbor Freight. Also, what do I need to connect it. I have a small compressor with the hose screwed into the compressor and the inflation valve on the end of the hose. Not sure of hose/fitting sizes.

[Tireman9]

Not sure why HF changed the link but here is the P/N if you need less than 90 psi: item#68215

1/4" pipe threads are standard on most air chucks. Also I keep mine in a ziplock bag so the desiccant is good all Summer.

There are similar products available at many auto parts stores. just ask for air dryer for air tools.

Note the HF "filter" P/N 68224 is not a desiccant as it filters out moisture that has condensed in your compressor or air lines.

You have given me a good topic for a blog post. Give me a week or so to do the research.

[hermanmullins]

1/4 NPT threads on Air hose and connections. There are two different quick disconnects. I have adapter for both in the coach. I use the double ended air chuck and a truck pressure gauge.
It all works for me.

Happy inflating.

Herman

[rogelling]

Not being an engineer or a physicist ( I'm just a country doctor), I was flat wrong about the relative humidity of compressed air. In reviewing my medical physics and some technical websites I have come to realize that the dew point of water vapor is what matters when compressing air. The partial pressure of water vapor is going to increase proportional to the change in pressure of the compressed air, so that the dew point will also increase. Assuming the temp stays fairly constant, the air in your 120 psi tank is going to become saturated at room temp and because the dew point temp will increase to about 70F it is likely that some of the water will condense in the tank, so now the compressed gas is saturated (relative humidity is 100%) but the actual water content is less because of condensation in the tank.

When it comes to tank air or oxygen, because the pressures are so high, 2500-3000 psi, the dew point would be much higher than room temp and moisture would form inside the tank causing corrosion, so theses gases are dried before being compressed into the tank. I suppose this is the real advantage of nitrogen (tank gas compressed to 3000psi with zero water vapor) vs compressed air to 120psi.

"4. Why is knowledge of dew point in
compressed air important?
The importance of dew point temperature in compressed
air depends on the intended use of the air. In many
cases dew point is not critical (portable compressors for
pneumatic tools, gas station tire filling systems, etc.).
In some cases, dew point is important only because
the pipes that carry the air are exposed to freezing
temperatures, where a high dew point could result in
freezing and blockage of the pipes. . In many modern factories, compressed air is used to operate a variety
of equipment, some of which may malfunction if
condensation forms on internal parts. Certain water
sensitive processes (e.g. paint spraying) that require
compressed air may have specific dryness specifications.
Finally, medical and pharmaceutical processes may treat
water vapor and other gases as contaminants, requiring a
very high level of purity.

http://www.vaisala.c...1EN-A-LoRes.pdf

[wolfe10]

The good news is that most coaches with air brakes and/or air suspensions have AIR DRYERS between the on-engine air compressor and the tanks that feed the other systems.

[Tireman9]

I posted some information on how to get reasonably dry air for your tires if the change in pressure is of concern to you.
http://www.rvtiresaf...your-tires.html

To help everyone here is what really happens to the "air" in your tires.
The Nitrogen is less reactive than the Oxygen so the Oxygen tends to migrate through the rubber at a faster rate than the other gasses. In general all tires will loose from 1% to 3% pressure each month when all the variables are controlled in the laboratory. Temperature change has the biggest effect on pressure but Elivation and Barometric pressure also have an effect.

We have run experiments where we measure the %N2 in a tire and over a period of a year as the O2 "leaks" out and more air is added to maintain the tire inflation level the net effect is to increase the % N2 in the tire air chamber by a couple %. This is measurable but not really meaningful in the big picture. By the time you increased the N2 % to say 82 or 84% the tires would probably be be worn out or over age.

[QuiGonJohn]

Tireman, it sounds like you are saying that, if I got new tires recently and they filled them with nitrogen, I could use regular air, (when I need to top them off), (dried if possible), and overtime, (due to the oxygen "leaking out"), I would not be decreasing the percentage of nitrogen in the tire. That in fact, over time this percentage will still increase very slightly.

[RVerOnTheMove]

I am hoping that what tireman is saying is Nitrogen in your tires is a scam. Just fill your tires with "dry" air and your results will be just about as good as filling your tires with Nitrogen. If that's not what he is saying, it is what he should be saying.

I have filled my tires with "air" for the last 15 years and I have never had any kind of a failure that could be attributed to over/under inflation, hot/cold tires or excess moisture. Sometimes, things just go wrong and something things go great forever. Nitrogen is not going to change any of those statistics.